Gabriele Tarquini admits Honda must improve after what he deemed to be a backward step in the 2013 World Touring Car Championship opener at Monza.
Tarquini says he expected far more performance following a podium in the 2012 Macau season finale and a winter of subsequent development.
While he salvaged third place in the second race and left Monza third in the points, Tarquini felt Sunday's rain had helped to negate Honda's performance deficit.
In the dry he had qualified more than 1.4 seconds adrift of poleman Yvan Muller.
"In these difficult conditions top speed not as important as the dry, but it seems the car is even slower than last year," Tarquini said.
"We knew we had a problem with top speed, but it's a big problem. We must improve."
Tarquini added that the fact Honda was still working to find the root of its problems could affect its form in the second round in Marrakech.
"We know the problem, but we don't know the cause - the engine has improved but the speed hasn't," he said.
"At the moment, if we don't solve this problem, Marrakech and the Salzburgring will be the worst for us. If we stay like this all season it will be tough.
"I expect to improve though; there is no reason we wouldn't.
"We will collect all the data and analyse it, we have our test car; we have everything to improve. We must do so."